The present invention relates generally to pulse combustion furnaces, and more particularly to an improved air flapper valve assembly for use in association therewith, such improved air flapper valve assembly having a valve body formed from an elastomeric material which results in significant reduction in audible sound and vibration.
Problems associated with less efficient prior art furnaces have been substantially ameliorated with the development of the pulse combustion furnace, wherein the fuel is burned in separate distinct "pulses", rather than in a continuously burning flame. In the pulse combustion furnace, the combustion air is drawn in from outside, and the combustion products are vented to the outside, both of which are entirely independent of and thus have no opportunity to enter the conditioned space. In addition, the pulse combustion process has the benefit of utilizing a minimum amount of heat exchanger material in order to transfer the heat released during the combustion process, due to the inherent nature of the pulsating flow as being turbulent, which accordingly enhances the heat transfer characteristics inherent in the pulse combustion process. In addition, the pulse combustion process permits the flexibility of firing at various input rates, and also produces reduced amounts of nitrous oxide emissions, as compared with prior art systems.
However, certain difficulties or deficiencies have been noted in the otherwise greatly beneficial pulse combustion process. Most notably, noise associated with the pulse combustion process has proved to be a difficult and continuing challenge. In particular, a bare pulse combustion burner with no sound attenuation apparatus can emit a sound level of 90 to 100 dbA in the vicinity of the device. As the acceptable indoor sound level is only 65 dbA, attenuation of the emitted sound to about 1% of the bare burner level sound has been necessitated. Moreover, low frequency sounds associated with various vibrations with regard to the pulse burner have likewise proved to be difficult of reduction, and have in the past only been attenuated effectively by the use of considerable mass in the sound absorbance shielding apparatus. A secondary problem has been the generation of harmonic frequencies caused by the 60 Hz fire rate. One contributor to the substantial level of sound associated with pulse combustion furnaces has been the air flapper valves used in connection therewith. For example, a substantial level of sound generation has been associated with the opening and closing of these prior art air flapper valves with each pulse.
Lennox Industries Inc., the assignee hereof, has been an industry-wide leader in pulse combustion furnace technology and in associated sound attenuation equipment. Notwithstanding the previous improvements in sound reduction accomplished with regard to advanced pulse combustion furnace design, further reduction in sound has been desirable in the art. Thus, in view of the prior art problems associated especially with sound reduction in regard to pulse combustion furnaces, it is a material object of the present invention to provide an improved air flapper valve assembly for use in association with a pulse combustion furnace which will substantially reduce the sound and vibration emanating from pulse combustion furnaces.
It is a further object of the improved air flapper valve assembly of the present invention to provide an air flapper valve assembly having a valve body formed from an elastomeric material which has a defined hardness and a defined thermal resistance thereby to give rise to the desired characteristics.